1. Field of the Invention
The present invention relates to an organic electroluminescence element.
2. Description of the Related Art
Organic electroluminescence elements are widely used in displays, backlights, and lighting applications, for example.
In general, an organic electroluminescence (EL) element includes an anode, a cathode, and an organic light emitting layer arranged between these electrodes. When a voltage is applied between the electrodes, holes and electrons are injected into the organic light emitting layer from the electrodes. When the electrons and the holes are recombined in the organic light emitting layer, binding energy is generated, and the organic luminescent material within the organic light emitting layer is excited by the binding energy. Light is emitted when the luminescent material returns to the ground state from the excited state, and such a mechanism is used to obtain a light emitting element.
Typically, the organic EL element further includes a hole injection layer and/or hole transport layer, and an electron injection layer and/or electron transport layer. The hole injection layer and/or hole transport layer is arranged between the anode and the organic light emitting layer and is configured to selectively inject holes into the organic light emitting layer. The electron injection layer and/or electron transport layer is arranged between the cathode and the organic light emitting layer and is configured to selectively inject electrons into the organic light emitting layer. Thus, by arranging these layers in the organic EL element, light emitting efficiency of the organic EL element may be improved (see e.g. Japanese Laid-Open Patent Publication No. 11-102787).
In the organic EL element as described above, a material such as lithium fluoride (LiF) is typically used in the electron injection layer.
However, because lithium fluoride is an insulating material, when this material is used in the electron injection layer of an organic EL element, the layer thickness has to be extremely thin (e.g. 0.1 nm to 0.4 nm). Forming such a thin film is often quite difficult. For example, when the film thickness is too thin, it may be difficult to obtain a layered thin film. On the other hand, when the film thickness to too thick, an electron injection layer with adequate conductivity may not be obtained.
Also, lithium fluoride is relatively unstable and is prone to degradation upon coming into contact with the atmosphere. Thus, an electron injection layer made of lithium fluoride needs to be handled under a controlled environment, and as a result, the fabrication process thereof may be complicated.
Further, when the electron injection layer fails to achieve adequate conductivity or is degraded due to the above characteristics of lithium fluoride, desired light emitting characteristics may not be obtained in the organic EL element, or the reliability of the organic EL element may be degraded.
In view of the above, an aspect of the present invention relates to providing an organic electroluminescence element with improved stability and reliability.